Will Legislative Changes Fix the Real Problem of Data Cables Overheating?George Brooks
Did you know the origins of the NEC can be traced back to the 1893 World’s Fair, where controversy over Thomas Edison’s DC current prompted local authorities to begin discussing safety procedures? Flash forward 127 years to today; man’s use of electricity has taken quantum leaps forward. If he were alive, Edison probably would be astonished at the progress.
But one thing remains constant. The code is still all about safety. Many states, counties and municipalities still adopt the NEC with the aim of limiting fires and preventing electrical hazards.
As technology advances, so too does the NEC, which is updated every three years. One recent example is the revision to the 2017 NEC and addition of Section 725.144 to ensure that Class 2 and Class 3 data cables supporting PoE applications do not exceed their temperature rating. The anticipated demand for higher-power PoE devices helped precipitate this change.
In the aftermath of these changes, several states introduced proposed legislation that would alter licensure requirements for installation. Specifically, those who install data cabling and equipment that support PoE applications would be required to hold an electrical license granted by state authorities.
Aside from the pros and cons of any single piece of legislation, two issues deserve careful consideration:
- Will legislation impose limitations on installation companies and result in higher end-user costs?
- Will legislation address the concern over data cables overheating when used for PoE applications?
Free and efficient markets work best when consumers have multiple options to choose from. The same holds true in the cabling industry, where end-users have multiple choices and access to a large and diverse pool of companies that provide installation services. The question is, will legislation result in them incurring a higher cost for installation labor . . . and lead to higher costs for their customers? There is another, perhaps more important, issue at stake here and that is whether legislative proposals are addressing the right concern. A closer look at a PoE circuit helps explain why.
Structured Cabling for PoE
One of the differences between a PoE circuit and a traditional electrical circuit is that the PoE source applies voltage only after a handshake negotiation occurs between the Power Sourcing Equipment (PSE) and a Powered Device (PD). Both kinds of circuits can overheat when exceeding their rated current carrying capacity.
If instead of legislatively trying to find a fix for which such proposals may not be the answer, what if a solution could be developed that would provide a safety net?
For the traditional electrical circuit, this concern was overcome with the development of the idea for a circuit breaker by Edison, the invention of the automatic circuit breaker in 1900 by Granville Woods, and subsequent inventions and derivative work. The circuit breaker provided a safety measure for preventing the overheating of electrical cables, thus protecting commercial and residential structures.
As illustrated in Figure 1 below, the circuit breaker panel is placed between the power source and the electrical outlet to stop the flow of current when too much current is drawn. Electrical outlets are connected in series with the circuit breaker panel and electrical cables are not bundled in groups.
For the PoE circuit, a PoE breaker panel is a technology that mimics the electrical circuit breaker panel. It can be a solution for overcoming the concern with data cables overheating due to exceeding their rated current carrying capacity. As illustrated in Figure 2, the PoE breaker panel is placed between the PoE source and PoE outlet in a similar fashion as the circuit breaker in Figure 1. The difference is that PoE outlets are connected in parallel with the PoE breaker panel and data cables are bundled in groups. Thus, the bundling of cables and current will cause the cable temperature to rise.
Network Safety Compliance
As states, counties, and municipalities move forward with adopting the 2017 edition of the NEC and legislative activities abound, it is important to consider whether or not licensure bills will result in a solution that addresses the concern with data cables overheating. It is also important to assess these activities from the standpoint of their impact on end-users.
Regardless of whether or not licensure bills are passed, a PoE breaker panel can address the major concern that data cables can overheat, just as the circuit breaker did for electrical cables. It may also be the most practical way to provide an Authority Having Jurisdiction (AHJ) with the ability to confidently certify cable installations. And last but not least, it can help end-users avoid higher installation cost by allowing them to maintain their current pool of companies for contract installation services.